1. Field of the Invention
The present invention relates to coated ophthalmic lenses and to the method of applying a coating to such lenses, and in particular, it relates to applying a thin abrasion-resistant coating to form a coated ophthalmic lens.
2. Description of the Prior Art
Optically clear, polymerizable, cast or molded plastics having a high light transmission and low haze are increasingly preferred over glass for ophthalmic lens material due to lighter weight, higher impact resistance and breakage resistance, as well as lower manufacturing costs in high-volume applications. Optical elements and lenses of uncoated plastics, however, suffer by comparison to glass from poor resistance to abrasion, scratching and marring which results in surface haze and poor image quality as well as low resistance to some common chemicals and solvents. Numerous commercial products have been introduced which have a hard coating to protect the plastic lens.
Conventional methods of applying such hard coating compositions employ flow coating, dipping, spraying, spin coating, curtain coating, and various other methods. All of these methods apply the coating to a previously formed or shaped, molded or cast plastic optical element or lens. However, certain advantages exist for applying the hard coating composition into the mold before casting or molding takes place, then partially or fully polymerizing the coating with the coating adhering to the molded plastic optical element at the time of removal from the mold. Examples of in-mold coating processes for forming labels on plastic containers are described in the following patents:
______________________________________ Inventor Patent No. ______________________________________ Ross 4,498,854 Bartimes et al 4,479,644 Slat et al 4,479,770 Slat et al 4,479,771 ______________________________________
Examples of in-mold processes which provide a decorative or protective coating on nonoptical thermoset molded plastics or plastic parts are described in the following patents:
______________________________________ Inventor Patent No. ______________________________________ Verwer et al 4,517,235 Ungar et al 4,520,062 Makhlouf et al 4,477,405 Modur et al 4,443,177 Ungar et al 4,499,235 Monnet 4,497,763 Griffith et al 4,438,062 Hamner 4,515,543 Cobbledick 4,515,710 Cobbledick et al 4,508,785 ______________________________________
Hard coating of polymethyl methacrylate (PMMA) cell-cast acrylic sheet windows is described in Japanese Pat. No. 74-45965 issued on May 2, 1974 to Oshima et al. The coating is applied in-mold and is subjected to a plurality of exposures to actinic or ultraviolet radiation before filling the mold with a suitable polymerizable resin. The coating is cured in situ with the acrylic sheet. One drawback to this process is that the freshly coated mold is blanketed with an inert gas atmosphere before exposing the ultraviolet-curable coating composition to an ultraviolet radiation source.
The Oshima et al U.S. Pat. No. 3,968,305 also describes providing a protective coating layer to acrylic sheet windows. Preferred coating compositions include trimethylolethane triacrylate, trimethylolpropane triacrylate, pentaerythritol tetracrylate. The coating is polymerized preferably by ultraviolet rays with the polymerization carried out in noncontact with oxygen. A photosensitizer is used, capable of activating the polymerizable coating material at a wavelength ranging from 3000 to 4000 A, to produce a radical with a preferred photosensitizer being a carbonyl compound. After the coating composition is placed on the mold surface, a film having little or no affinity for the coating composition is made to adhere closely to the coating composition to ensure that no air bubbles are left thereby preventing the coating composition from coming into contact with oxygen. After the coating composition is cured to the degree desired, the film is removed and monomer for the formation of the polymeric body of the article is disposed on the coated cured composition. Although the coating material is polymerized to a great degree, there is adhesion of the surface layer to the resin forming the shaped article.
The Matsuo et al U.S. Pat. No. 3,968,309 describes a process for applying an abrasion resistant coating on a substrate of plastic. The coating consists of at least 30% by weight of polyfunctional compounds selected from the group consisting of polymethacryloyloxy compounds having at least three methacryloyloxy groups in one molecule with the molecules having a molecular weight of 250 to 800 and polyacryloyloxy compounds having at least 3 acryloyloxy groups in each molecule, and a fluorine-containing surfactant, in which the fluorine atom is bonded to a carbon atom. The coating is either applied to the already molded plastic substrate or is applied to the mold and the coating is cured by ultraviolet radiation in a nitrogen atmosphere.
The Russell U.S. Pat. No. 4,338,269 discloses an in-mold applied hard coating composition for the formation of a coated ophthalmic lens. The coating composition includes a pentaerythritol-based polyacrylate in combination with a cellulose ester or vinyl chloride-vinyl-acetate-containing copolymer (the function of which is to reduce surface oxygen inhibition during cure) followed by ultraviolet actinic radiation to form a cured abrasion-resistant coating in the presence of an ordinary oxygen-containing atmosphere. However, in order to obtain a satisfactory degree of crosslinking in the presence of ultraviolet radiation in an ordinary oxygen-containing environment, the Russell compositions contain a cellulose ester or a vinyl chloride-vinyl acetate containing copolymer in substantial proportion (on the order of 10% or more). Consequently, the Russell coating does not achieve the abrasion resistance that is presently desirable for ophthalmic lenses.
The Sandvig et al U.S. Pat. No. 4,544,572 describes an in-mold hard coated plastic ophthalmic lens which employs an ethylenically-reactive-unsaturated monomer/oligomer-containing formulation which is applied to a mold surface. Solvents in the formulation are volatilized and the formulation is brought to an intermediate degree of crosslinking by either heat or actinic radiation to form a dry tack-free film having sufficient adhesion and cohesive strength to the mold surface to permit further processing and to precisely replicate the mold surface so as to be free of optical defects. The coating at this point is in a soft-nonabrasion-resistant "gelled" polymer state. The lens forming material is then introduced into the mold and the lens forming material along with the coating composition is then subsequently crosslinked or hardened by heat. The lens is removed with the coating adhering to the fully polymerized plastic lens, both being in a fully cured state.